I've been quantifying and tracking random variables in my life (eg sleep, happiness) for the last ten years or so and have yet to find an app that allows me to do this the way I like, so I decided to build one. There are already a lot of apps like this out there and I'm testing them out every day to get an idea of what I like and don't like about them.
Here is my philosophy behind the app: I want something that is simple and can track anything. I want it to be minimally rigid, meaning the app doesn't decide how or what to track. You do.
There are two apps that I'm drawing inspiration from outside of the quantified self movement:
Trello: I'm copying the philosophy behind Trello of creating just the right amount of simplicity and complexity. It can be used for just about anything, however you want. There is minimal rigidity in the data and user experience. If you can quantify it (most things can at least be put into a scale of 1-10), then you can track it.
Day One: I love the interface. It does exactly what it needs to do and nothing more. It's not new: there are a million journaling apps out there, but they finally got it right. I would love to integrate my app with Day One at some point actually, so that you can combine quantitative logging with qualitative journaling.
I've built a grungy prototype as a proof of concept. If you are a Mac user, you can download and try it out: http://cjroth.github.io/lifetracker/
It's not awesome (yet), but shit, it's pretty decent for a start. Over the next months I'm planning on working on it as much as I can find the time to and make it perfect. I'm in the process of porting it to iOS and Android now too.
I am looking for a few initial power users to help me test and and give me feedback. I would also love it if you could take a few minutes to take this survey: http://goo.gl/forms/x8zzbDgUqU. I want to understand what sort of an app you want and how you plan to use it.
I'm particularly curious on what features you want to see, how you plan to use it, and how privacy and data ownership matter to you.